A recent study by researchers at Emory's Rollins School of Public Health and the Colorado School of Public Health determined that both climate and heavy rainfall along with social variables are key factors in determining cases of waterborne diarrhea.

Researchers analyzed a large dataset on weekly cases of diarrhea over more than three years, along with rainfall data and social variables throughout 19 villages in Ecuador. Findings determined that heavy rainfall was associated with increased cases of diarrhea when it occurred after a dry period but decreased cases of diarrhea when it occurred after a wet period.

Complete findings are available in the November 20th, online edition of the Journal of Epidemiology at: http://aje.oxfordjournals.org/content/early/2013/11/19/aje.kwt279.abstract 

"During dry periods, pathogens accumulate in the environment and when a heavy rain event occurs it can spread them through the village," explains Karen Levy, PhD, co-author and assistant professor in the Department of Environmental Health at Emory's Rollins School of Public Health. "People ingest these pathogens when they consume untreated drinking water and this can increase diarrhea incidence. But during wet periods, the pathogens may be regularly flushed from the village environment, and heavy rainfall can further dilute their concentration, which means fewer people will be exposed to pathogens."

In addition to biophysical conditions, the team also found that the health impacts of heavy rainfall were reduced in communities where more people treated their drinking water.

"Investments in public health infrastructure like water treatment, whether in the community or in the home, can remove pathogens circulating in the community, reducing transmission," states lead researcher Elizabeth Carlton, PhD, assistant professor of Environmental Health at the Colorado School of Public Health. "Our findings underscore the need to account for both social and biophysical factors when evaluating the effects of climate on disease."